The present invention relates to electric heating blankets, pads and pillows.
Present day warming blankets typically include a safety circuit for interrupting or cutting off electrical power to the blanket in the event of an electrical fault such as arcing, a short circuit or an open circuit.
Conventional safety circuits measure voltage at the remote end of the heating wire, i.e., the end farthest from where the wire enters the blanket. This form of measurement requires a safety circuit module to be located inside the blanket or an additional pair of wires must be returned to the controller located on the exterior of the blanket. This requires the heating wire to complete a full circuit loop within the blanket and return back to the edge of the blanket where the resistance heating wire is connected to an external power cord. This connection requires an additional electrical connector pin or pins.
It would be advantageous to be able to externally measure only the current entering a warming blanket or pad in order to detect an electrical fault in the resistance/heating wire. This would be particularly advantageous in the case of resistance wire fabricated from PTC (positive temperature coefficient) wire. In this case a complete looped circuit would not be required and a simplified and more economical blanket construction would be enabled.
In any case, by measuring the current entering the blanket, a safety circuit can be located remotely and externally of the blanket.
The invention has been developed to fulfill the needs noted above. A primary object of the invention is to provide an electric fault detector positioned externally from a heating blanket without the need for extending one or more wires back to the external controller. This object is achieved by locating most of the fault detecting electronics in an application specific integrated circuit (ASIC). This reduces both the safety circuit size and its cost.
The resulting safety circuit can be located on a controller or near an electrical connector, i.e., near a wall plug, if desired. The combination of the safety circuit and the wall plug can be molded as a single compact module, if desired. By positioning the safety circuit at the wall plug and measuring electrical faults at this point, faults between the wall plug and blanket can be immediately detected, i.e., faults in the power cord. Prior safety circuits located at the blanket could not detect such faults.